Communication system and communication controlling method

ABSTRACT

A communication method in LIPA/SIPTO architecture is provided which, when a user equipment (UE) is to connect from a serving area to an external network, allows re-selection of an optimal gateway. The communication method allows selecting a gateway apparatus physically or topologically close to a site, where the user equipment is attached.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. Nos.13/149,264 and 13/118,743, filed May 31, 2011, which are divisionals ofU.S. patent application Ser. No. 13/131,810, filed May 27, 2011, whichis an national stage of International Application No. PCT/JP2010/066211,filed Sep. 17, 2010, claiming priority based on Japanese PatentApplication No. 2009-217757, filed Sep. 18, 2009, the contents of allwhich are incorporated herein by reference in their entirety.

TECHNICAL FIELD

This invention relates to a mobile communication system and, moreparticularly, to a system optimal for re-selection of a gateway thatconnects a terminal to a packet data network. This invention alsorelates to a communication controlling method.

BACKGROUND

In EPC (Evolved Packet Core), bearer management is performed based on an‘Always On’ concept in such a manner that a PGW (PDN (Packet DataNetwork) Gateway), initially selected when a UE (User Equipment or‘terminal’) has attached the EPC, is fixedly used as anchor until the UEdetaches. By this manner of operation, it is possible for a servicenetwork (a packet data network) to provide services premised onpermanent connection. It is because the IP information driven out by thePGW is unchanged even if the UE moves repeatedly within the EPC.

When a UE moves within the EPC, an SGW (Serving Gateway) is re-selectedin accompaniment with the movement of the UE. Each time the SGW isre-selected, a bearer between the SGW and the PGW is updated bydisconnection and re-establishment to ensure connectivity from the UE tothe PGW.

In general, in selecting a PGW, such a PGW is selected which is close tothe SGW physically or from the perspective of network topology.

However, in case the UE performs repeated movement over long distancesor has stayed in a far-away place after such long-distance movement, thePGW, initially selected, may be far away from a SGW in terms of adistance(a physical or network topological distance). As a result,network efficiency is deteriorated to present problems such astransmission delay of user data or inefficient consumption of networkresources within the EPC.

For example, when a passenger to Japan from abroad enters at NaritaInternational Airport, he/she may usually power-up the mobile phoneapparatus at the International Airport to attach to EPC. Hence, a PGWlocated close to Narita International Airport is selected. However,after entrance to Japan, he/she may move to e.g., Tokyo, Osaka, Sapporoor Fukuoka. Hence, after each such movement, the PGW close to the NaritaInternational Airport is no longer the most efficient PGW.

SUMMARY

The following is an analysis by the present inventors. In the EPCnetwork, a default bearer, established at the time of attachment, is notdeleted/re-established until the time of detachment under the ‘AlwaysOn’ principle. If the bearer is to be switched due to UE's movement, thePGW, selected at the time of attachment, remains fixed as anchor.

Consequently, such a problem is raised that, when a UE moves over a longdistance, maintaining connection to the PGW selected at the time of theattachment may be inefficient from the perspective of EPC network.

Such a system is thus desired that, when a UE moves over a longdistance, and the UE is to connect from a serving area in which the UEresides to an external network (service network), allows re-selecting anoptimal PGW (result of analysis by the present inventors).

It is therefore an object of the present invention to provide a systemand a method, which make it possible to re-select an optimal gatewaynode, when a terminal (UE) is to connect from a serving area to anexternal network.

In one aspect of the present invention, there is provided In one aspectof the present invention, there is provided a communication method inLocal IP Access (LIPA)/Selected IP Traffic Offload (SIPTO) architecture,wherein a gateway apparatus physically or topologically close to a site,where the user equipment is attached, is selected according to movementof the user equipment.

According to the present invention, there is provided a communicationsystem in Local IP Access (LIPA)/Selected IP Traffic Offload (SIPTO)architecture, wherein a gateway apparatus physically or topologicallyclose to a site, where the user equipment is attached, is selected,according to movement of the user equipment.

According to the present invention, there is provided user equipment ina communication system by Local IP Access (LIPA)/Selected IP TrafficOffload (SIPTO) architecture, wherein a gateway apparatus physically ortopologically close to a site, where the user equipment is attached, isselected, according to movement of the user equipment.

In another aspect of the present invention, there is provided acommunication method in Local IP Access (LIPA)/Selected IP TrafficOffload (SIPTO) architecture, wherein, in case a mobility managemententity (MME) decides that it is necessary to re-select a gatewayapparatus, the MME sends a first signal for setting re-attachment to auser equipment, the user equipment on receipt of the first signaltransmitting a second signal for re-attachment to the MME and the MMEre-selecting the gateway apparatus.

According to the present invention, there is provided a communicationsystem in Local IP Access (LIPA)/Selected IP Traffic Offload (SIPTO)architecture, comprising a mobility management entity (MME) and a userequipment, wherein the MME sends a first signal for settingre-attachment, when the MME decides that it is necessary to re-select agateway apparatus, the user equipment transmits a second signal forre-attachment to the MME, on receipt of the first signal, and the MMEre-selects the gateway apparatus.

According to the present invention, there is provided a user equipmentin a communication system by Local IP Access (LIPA)/Selected IP TrafficOffload (SIPTO) architecture, wherein the user equipment receives afirst signal that sets re-attachment from a mobility management entity(MME) and transmits a second signal for re-attachment to the MME tocause re-selection of a gateway apparatus to be performed.

In yet another aspect of the present invention, there is provided acommunication method in Local IP Access (LIPA)/Selected IP TrafficOffload (SIPTO) architecture, wherein the method comprises:

-   -   a Serving General Packet Radio Service Support Node (SGSN)        sending a deactivate request for requesting re-selection, to a        radio access apparatus, when the SGSN decides that it is        necessary to re-select a gateway apparatus;    -   the radio access apparatus transmitting an RRC connection        reconfiguration to a user equipment;    -   the user equipment transmitting a notification of completion of        an RRC connection reconfiguration to the radio access apparatus;    -   the radio access apparatus transmitting a deactivate response to        the SGSN; and    -   the user equipment initiating a UE requested PDN connectivity        procedure, the gateway apparatus being re-selected.

According to the present invention, there is provided a communicationsystem in Local IP Access (LIPA)/Selected IP Traffic Offload (SIPTO)architecture, comprising:

-   -   a Serving General Packet Radio Service Support Node (SGSN);    -   a radio access apparatus; and    -   a user equipment, wherein    -   the SGSN sends a deactivate request for requesting re-selection        to the radio access apparatus, when the SGSN decides that it is        necessary to re-select a gateway apparatus,    -   the radio access apparatus transmits an RRC connection        reconfiguration to the user equipment,    -   the user equipment transmits a notification of completion of the        RRC connection reconfiguration to the radio access apparatus,        and    -   the radio access apparatus transmits a deactivate response to        the SGSN, and    -   the user equipment initiates a UE requested PDN connectivity        procedure to cause the SGSN to re-select the gateway apparatus.

According to the present invention, there is provided a user equipmentin a communication system by Local IP Access (LIPA)/Selected IP TrafficOffload (SIPTO) architecture, characterized in that on receipt of an RRCconnection reconfiguration from a radio access apparatus, the userequipment transmits a notification of completion of RRC connectionreconfiguration to the radio access apparatus to initiate a UE requestedPDN connectivity procedure to cause re-selection of a gateway apparatusto be performed.

According to the present invention, it is possible to re-select anoptimal gateway node at a time when a user equipment is to connect froma serving area to an external network (service network).

Still other features and advantages of the present invention will becomereadily apparent to those skilled in this art from the followingdetailed description in conjunction with the accompanying drawingswherein only exemplary embodiments of the invention are shown anddescribed, simply by way of illustration of the best mode contemplatedof carrying out this invention. As will be realized, the invention iscapable of other and different embodiments, and its several details arecapable of modifications in various obvious respects, all withoutdeparting from the invention. Accordingly, the drawing and descriptionare to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a entire configuration of a system accordingto an exemplary embodiment of the present invention.

FIG. 2 is a diagram for explaining a Comparative Example.

FIG. 3 is a diagram for explaining the present invention.

FIG. 4 is a diagram illustrating a sequence of the Comparative Example.

FIG. 5 is a diagram illustrating a sequence of an exemplary embodiment 1of the present invention.

FIG. 6 is a diagram illustrating a sequence of an exemplary embodiment 2of the present invention.

FIG. 7 is a diagram illustrating a sequence of an exemplary embodiment 3of the present invention.

FIG. 8 is a diagram illustrating a sequence of an exemplary embodiment 4of the present invention.

FIG. 9 is a diagram showing a configuration of an exemplary embodiment 5of the present invention.

FIG. 10 is a diagram showing a configuration of an exemplary embodiment6 of the present invention.

FIG. 11 is a diagram illustrating a sequence of the exemplary embodiment5 of the present invention.

FIG. 12 is a diagram illustrating a sequence of the exemplary embodiment6 of the present invention.

FIG. 13 is a diagram illustrating a sequence of an exemplary embodiment7 of the present invention.

FIG. 14 is a diagram illustrating a sequence of an exemplary embodiment8 of the present invention.

PREFERRED MODES

The following describes exemplary embodiments of the present inventionwill now be described. A system according to one of modes of the presentinvention re-selects a PGW (PDN gateway) in EPC in keeping with movementof a user equipment (UE) and re-establishes a default bearer, therebyrealizing improvement of transmission delay and efficiency of networkresources in the EPC.

In current 3GPP standardization, such techniques, termed LIPA (Local IPAccess) or SIPTO (Selected IP Traffic Offload), are under study. Inthese techniques, user traffic is not taken into EPC and is made to havedirect access to an external packet network from a radio access network,in which a UE resides. In case the present invention is adapted tocooperate with the LIPA/SIPTO architecture, it becomes possible torealize efficient utilization of network resource more effectively.

In a system according to an exemplary embodiment of the presentinvention, a PGW is re-selected for a UE which is being attached to theEPC.

An EPC bearer usually uses in a fixed manner, a PGW which is initiallyselected when a UE is attached (registered) to the EPC network, as ananchor, until the UE is detached (deleted from registration). However,in case the UE moves over a long distance, it may occur frequently thatthe PGW initially selected ceases to be a most efficient gatewayapparatus for the external network.

In one of modes of the present invention, a path (bearer) between a UEand a PGW may be optimized by re-selecting and modifying the PGW, suchas when the UE is in an idle state.

In one of modes of the present invention, a default bearer isre-established, with the re-selection of as the PGW, when the UE is notinvolved in packet communication, i.e., when the UE is in idle mode. Byso doing, network resources between UE and PGW may be optimized withoutdetracting from the user experience.

The following describes the operation in case the UE moved astride anSGW. FIG. 2 shows, as Comparative Example, a case where the presentinvention is not applied. Referring to FIG. 2, since the UE is attachedto an SGW 61 on the left side of FIG. 2, a PGW 71, which is closer tothe left side SGW 61 in a physical distance or a network-topologicaldistance, is initially selected, and a connection path 1 is set. Whenthe UE is moved a long distance, the UE continues to use the left-sidePGW 71. Hence, the UE and the PGW are connected by an inefficientconnection path 2.

In contrast, FIG. 3 shows a case where the UE moves astride the SGW, asthe present invention is applied. Referring to FIG. 3, since the UE isattached to the SGW 61 on the left side of FIG. 3, the PGW 71, closer tothe left side SGW 61 in a physical distance or a network-topologicaldistance, is initially selected, and a connection path 3 is set. The EPCthen re-examines the connectivity between the UE and the externalnetwork (service network), using the UE's movement over the largedistance as a trigger. As a result of the re-check, the EPC gives adecision that a right-side PGW2 provides a more efficient connection(UE-PGW path) than the left-side PGW 71. Hence, the path between the UEand the PGW is changed over from the connection path 3 to the connectionpath 4, thus assuring more efficient connection. The present inventionwill now be described with reference to exemplary embodiments.

Exemplary Embodiment 1

FIG. 1 shows the arrangement of a network system according of thepresent exemplary embodiment. The basic arrangement itself of thenetwork remains unchanged from a hitherto-used EPC network arrangement.

Referring to FIG. 1, UE1 to UE3 are mobile phones. In FIG. 1, eNodeB(evolved Node B) are base stations of LTE (Long Term Evolution), whileNodeB 21 and RNC (Radio Network Controller) 31 are apparatuses for radioaccess adopted in the UMTS (Universal Mobile Telecommunication System).

An MME (Mobility Management Entity) 41 is an apparatus for mobilitymanagement as introduced by EPC.

An SGSN (Serving GPRS (General Packet Radio Service) Support Node) 51 isa serving apparatus, used for UMTS, and may or may not handle a userplane processing, depending on a connection modes.

In case the SGSN does not handle a user plane, the user plane is setbetween the SGW (Serving Gateway) and the RNC.

SGWs 61 and 62 are serving apparatuses that may handle the user plane.PGW 71 and 72 are gateway apparatuses that connect an external network(a service network 81 in the drawing) and RNC.

The following describes the operation of the present exemplaryembodiment. Initially, an update procedure of a tracking area (TA UpdateProcedure) will be described with reference to a Comparative Example towhich the present invention is not applied.

FIG. 4 shows a case of TA update accompanied by SGW change (ComparativeExample). It is noted that, when a UE is in idle condition, that is, ina no-connection state, it is managed to which tracking area (positionregistration area) the UE belongs, however, it is not managed in whichcell the UE resides.

MME receives a TA update request (TA Update Request) from the UE and, ifit is determined that SGW needs to be changed, a create session request(Create Session Request) is sent to an SGW (2) which is a change-targetSGW.

The SGW (2) sends a modify bearer request (Modify Bearer Request) to thePGW (1) to notify the PGW (1) of the fact that the SGW as destination ofconnection is changed.

On completion of update of the bearer context information, the PGW (1)sends a response to the modify bearer request (Modify Bearer Response)to the SGW (2).

On receipt of the response to the modify bearer request (Modify BearerResponse) from the PGW (1), the SGW (2) sends a create session response(Create Session Response) to the MME.

On receipt of the create session response (normal response) from the SGW(2), the MME sends a delete session request (Delete Session Request) tothe SGW (1), which is a change-source SGW.

After deletion of the bearer context, the SGW (1) sends a delete sessionresponse (Delete Session Response) to the MME.

On receipt of the delete session response (Delete Session Response) fromthe SGW (1), the MME sends a TA (Tracking Access) accept (TA accept) tothe UE.

In contrast to the Comparative Example, shown in FIG. 4, the sequenceoperation shown in FIG. 5 is carried out in an exemplary embodiment ofthe present invention. The following describes the sequence of thepresent exemplary embodiment with reference to FIG. 5.

The MME receives a TA update request (TA Update Request) from the UE. Incase the MME decides that the SGW is to be changed, the MME sends acreate session request (Create Session Request) to the SWG (2) which isa change-target SGW.

In case the MME decides that PGW re-arrangement is necessary, the MMEselects a PGW (2) that can be efficiently connected to the externalnetwork (service network), and sets address information that identifiesthe PGW, in the create session request (Create Session Request).

The SGW (2), on receipt of the new PGW address, sends a create sessionrequest (Create Session Request) to the PGW (2).

The PGW (2), responsive to the create session request (Create SessionRequest) sent from the SGW (2), creates a bearer context. The PGW (2)also assigns a new IP address for the user to the UE. After completionof assignment of the new IP address for the user and creation of thebearer context, the PGW (2) sends a create session response (CreateSession Response) to the SGW (2).

The SGW (2), responsive to the create session response (Create SessionRequest) from the PGW (2), sends a delete session request (DeleteSession Request) to the PGW (1).

The PGW (1) deletes the bearer context and sends a delete sessionresponse (Delete Session Response) to the SGW (2).

The SGW (2), responsive to the delete session response (Delete SessionResponse) from the PGW (1), sends a create session response (CreateSession Response) to the MME.

The MME, responsive to a normal response from the SGW (2), sends adelete session request (Delete Session Request) to the SGW (1), which isthe change-source SGW.

After deleting bearer context, the SGW (1) sends a delete sessionresponse (Delete Session Response) to the MME.

On receipt of the response, the MME sends a TA update accept (TA UpdateAccept) to the user. The IP information, newly assigned to the user, isset in the TA Update Accept and notified to the UE.

In the foregoing, such a case has been explained in which GTPv2 protocol(GPRS (General Packet Radio Service) Tunneling Protocol v2) is usedbetween SGW and PGW. Similar functions may be implemented for such acase where PMIPv6 (Proxy Mobile IPv6) is used.

In case of using PMIPv6 between the SGW and the PGW, Proxy BindingUpdate is used in place of Create Session Request/Delete SessionRequest. Also, Proxy Binding Acknowledgement is used in place of CreateSession Response/Delete Session Response.

The sequence to re-select a PGW is as shown in FIG. 5. To implement theabove functions, it is necessary for an MME to re-select a PGW at anappropriate timing.

If, during when a UE is performing packet communication, a PGW connectedto a service network is changed, the information such as IP address ischanged for a communication counterpart of the UE. As a result, thepacket communication by the UE is disconnected. Thus, in the operationshown in FIG. 5, it is necessary to re-select a PGW, during when the UEis not performing packet communication, that is, during ECM (EPSConnection Management)-IDLE time).

FIG. 5 shows the operation when an SGW is changed. However, even in casean SGW is not changed, the basic operation is the same. The messagesequence, shown in FIG. 5, is explained using message names for a casewhere the communication between an SGW and a PGW is implemented inaccordance with GTP protocol. However, similar effects may also beobtained in case the communication between the SGW and the PGW isimplemented in accordance with PMIP (Proxy Mobile IP) protocol.

If, in FIG. 5, an SGSN is substituted for an MME, the operation is thatof PGW re-selection in case an access network is UMTS.

In the present exemplary embodiment, described above, the followingoperation and advantageous effect may be obtained.

The selection of PGW based on the position in which a UE resides becomespossible. Since a PGW which is of a physically short distance from theUE or network-topologically close to the UE is selected and connected tothe UE, network resources may be optimized by efficient connection.

User data transmission delay may be reduced by efficient path connectionbetween the UE and the PGW.

Cooperated with the LIPA/SIPTO architecture, it becomes possible toprovide packet communication services without user data being taken intothe EPC. Hence, it becomes possible for a mobile communication operatorto reduce a load of an EPC network apparatus.

Exemplary Embodiment 2

The following describes a second exemplary embodiment of the presentinvention with reference to FIG. 6. On receipt of a TA update request(TA Update Request), sent from a terminal (UE), MME examines whether ornot a PGW, to which the UE is connected, is appropriate.

FIG. 6 shows a status in which a UE is connected to a PGW (1) (an EPSbearer established between the UE and the PGW (1): EPS bearer originallyestablished).

In case the MME decides that re-selection of another suitable PGW isnecessary, the MME sets a cause value that urges re-attach in a TAupdate request (TA Update Request) to send a TA update reject (TA UpdateReject) to the UE.

In response to the TA update reject (TA Update Reject) from the MME, theUE sends an attach (ATTACH) signal to the MME. On receipt of the TAupdate reject (TA Update Reject), the MME is able to newly start up alogic for selecting a PGW, as a result of which an optimal PGW isre-selected.

In the example of FIG. 6, such a case is shown in which a PGW (2) isre-selected to perform a connection procedure to the PGW (2). That is, acreate session request (Create Session Request) from the MME is sent tothe SGM (2) and the create session request (Create Session Request) issent from the SGW (2) to the PGW (2). On receipt of a create sessionresponse (Create Session Response) from the PGW (2), the SGW (2) sendsthe create session response to the MME. MME sends a delete sessionrequest (Delete Session Request) to the SGW (1). The SGW (1) returns adelete session response (Delete Session Response) to the MME. On receiptof the delete session response, the MME returns TA Update Accept whichindicates the completion of TA update, to the terminal (UE).

In the present exemplary embodiment, the following operation andadvantageous effect may be obtained.

In the present exemplary embodiment 2, no impact is imposed on a UE inthe first exemplary embodiment, while minimum changes may sufficeinsofar as the EPC is concerned.

Exemplary Embodiment 3

The following describes a third exemplary embodiment of the presentinvention with reference to FIG. 7. In the present exemplary embodiment,the usual TA update procedure is slightly changed.

The sequence shown in FIG. 7 is a normal TA update procedure. As a pointof change in the present exemplary embodiment, completion of the TAupdate procedure is notified from an MME to a UE.

Referring to FIG. 7, on receipt of a TA update request (TA UpdateRequest) from the UE, the MME sends a create session request (CreateSession Request) to the SGW (2). A modify bearer request (Modify BearerRequest) is sent from the SGW (2) to the PGW (1). On receipt of a createsession response (Create Session Response) from the SGW (2), the MMEsends a delete session request (Delete Session Request) to the SGW (1).On receipt of the delete session response (Delete Session Response) fromthe SGW (1), the MME sends a TA update accept (TA Update Accept (PDN)).

In the present exemplary embodiment, new information, that is, PDN ofthe TA Update Accept (PDN) in FIG. 7, is added to a TA Update Acceptsignal to urge re-connection of the packet data network (PDN) which iscurrently in a connected state.

On receipt of the TA update accept (TA Update Accept) signal, added bythe new information (PDN), the UE recognizes the PDN (packet datanetwork) for re-connection, based on the information specified. It isnoted that a plurality of PDNs may sometimes be so added. For the PDN,the UE starts up a UE requested PDN Disconnection processing (processingof disconnection of the PDN as requested by the UE) or a UE requestedPDN connectivity processing (processing of connection of the PDN asrequested by the UE) to re-connect the packet data network (PDN).

In this re-connection of the packet data network (PDN), it is possiblefor the MME to newly start up the PGW selection logic. As a result, itis necessary to re-select an optimum PGW.

FIG. 7 shows the operation for the case where the SGW is changed.However, even when the SGW is not changed, the basic operation remainsthe same.

The present exemplary embodiment has the following operation andmeritorious effect:

According to the present exemplary embodiment, PGW re-connection may bemade without starting up ATTACH processing (re-attach).

Starting up ATACH processing means that, if there are a plurality of PDNconnections, processing for PGW re-selection is started up for theentire PDN connections, and hence the processing of a relatively largescale is invoked.

With the present exemplary embodiment, in contrast, only there-selection of the PGW needed may be made by EPC startup.

Exemplary Embodiment 4

The following described a fourth exemplary embodiment of the presentinvention with reference to FIG. 8. In the fourth exemplary embodimentof the present invention, PGW re-selection, which may be started up bythe EPC (MME) at an optional timing, is made in a manner not dependentupon the TA update procedure carried out by the UE. If, when the MME isin a connected state, PGW re-selection is decided to be necessary, aPage signal is sent to the UE and the connection with the UE is tried.

It is noted that the cause information (reason information) is added asan option to the Page signal. See Page (cause) of FIG. 8. The UE isallowed to neglect this Page signal (Page signal with the causeinformation). This is a measure taken in order to avoid batteryconsumption in the UE caused by iterative execution of this processing.

Inherently, the Page signal is a signal used for notification of anincoming call. In contrast, the Page signal, sent in case PGWre-selection is needed, is for enhancing the efficiency of theconnection path in the EPC, such that it may not be said to be anindispensable operation. On receipt of this Page signal, the UE sends aservice request (Service request) signal to the MME for communicationtherewith. The MME sends a deactivate bearer request (Deactivate Bearerrequest) from the MME to the eNodeB. The eNodeB sends an RRC connectionreconfiguration. On receipt of a notification of completion of the RRCconnection reconfiguration from the UE, the eNodeB sends a deactivatebearer response (Deactivate Bearer Response) to the MME.

The MME then disconnects the connection of the packet data network(PDN), for which PGW re-selection is necessary, to induce the procedureof UE requested packet data network connection from the UE (UE requestedPDN connectivity).

By carrying out this procedure, it becomes possible for the MME to newlystart up the PGW selection logic. Thus, as a result, re-selection ofsuitable PGW becomes necessary. For this procedure, the EPC (MME) isable to start up PGW re-connection at an optional timing. In this case,O&M (Operation and Maintenance), LIPA or SIPTO connection/disconnectionmay be used as a trigger.

In the present exemplary embodiment, such operation and meritoriouseffect may be obtained that the MME may re-select PGW at an optionaltiming.

Exemplary Embodiment 5

The following describes a utilization example of the present inventionto a LIPA or SIPTO architecture. FIGS. 9 and 10 show the arrangement ofthe present exemplary embodiment.

Referring to FIG. 9, UE1 to UE3 are mobile phone apparatuses. eNodeB 11and 12 are LTE base stations. NodeB 21 and RNC 31 are apparatuses forradio access (Radio Access) adopted by the UMTS system. An MME 41 is anapparatus introduced by EPC to manage the mobility. An SGSN 51 is aserving apparatus used for the UMTS, and may or may not handle a userplane depending upon connection configurations. In case the SGSN doesnot handle a user plane, the user plane is set between the SGW and theRNC.

SGWs 61 and 62 are apparatuses inside the service range that handle theuser plane. The PGW 71 and 72 are gateway apparatuses that interconnectthe external network (service network 81 in FIG. 9) and the EPC. LPGW(Local PGW 91 and 92) are gateway apparatuses that share certainportions in common with the eNodeB or that are located extremely closeto the eNodeB and to allow connection to the service network 81.

In FIG. 10, UE1 and UE2 are mobile phone apparatuses. NodeB 21 and 22and RNC 31 and 32 are apparatuses for radio access adopted in the UMTSsystem. SGSNs 61 and 62 are serving apparatuses and may or may nothandle the user plane depending upon connection configurations. In casethe SGSN does not handle a user plane, the user plane is set between theGGSN and RNC. It is noted that the configuration in which the user planeis set between the GGSN and RNC is called the ‘direct tunnelconnection’.

GGSNs 71 and 72 are gateway apparatuses that interconnect the externalnetwork (service network 81 in FIG. 10) and GPRS (General Packet RadioService) network.

LGGSNs (Local GGSNs (Gateway GPRS Support Nodes)) 101 and 102 aregateway apparatuses that share certain portions in common with or arelocated extremely close to the RNCs (Radio Network Controllers) and thatallow for connection to the service network 81.

The following describes the operation of the fifth exemplary embodimentshown in FIG. 9, with reference to the sequence diagram shown in FIG.11.

The MME receives a TA update request (TA Update Request) from the UE. Incase the architecture is that of LIPA or SIPTO, the TA update request(TA Update Request) signal from the eNodeB to the MME is encapsulated inthe S1-AP message for transmission.

At this time, the eNodeB notifies the MME on the S1-AP message of thefact that PDN connection may be set by the LIPA/SIPTO architecture.

In case the MME decides that the SGW needs to be changed, it sends acreate session request (Create Session Request) to the SGW (2) which isa change-target SGW.

In case the MME decides that re-arrangement to LPGW is necessary, theMME selects an LPGW that may efficiently be connected to the externalnetwork (service network 81), and sets address information thatdesignates the PGW, in the create session request (Create SessionRequest). It is noted that the above mentioned notification on the S1-APmessage that PDN connection may be set by the LIPA/SIPTO architecture isby way of illustration only such that it is also possible for the MME todecide on the necessity for re-selection based on some otherinformation.

On receipt of a new PGW address, the SGW (2) sends a create sessionrequest (Create Session Request) to the LPGW. On receipt of the createsession request (Create Session Request), the LPGW creates a bearercontext (Bearer Context).

The LPGW assigns a new IP address for the user to the UE.

On completion of assignment of the new IP address for the user andcreation of the bearer context (Bearer Context), the LPGW sends a createsession response (Create Session Response) to the SGW (2).

On receipt of the create session response (Create Session Response), theSGW (2) sends a delete session request (Delete Session Request) to thePGW(1).

The PGW (1) deletes the bearer context (Bearer Context) and sends adelete session response (Delete Session Response) to the SGW (2).

On receipt of the delete session response (Delete Session Response), theSGW (2) sends a create session response (Create Session Response) to theMME.

On receipt of the normal response from the LPGW, the MME sends a deletesession request (Delete Session Request) to the SGW (1), a change-sourceSGW.

After deleting the bearer context (Bearer Context), the SGW (1) sends adelete session response (Delete Session Response) to the MME.

On receipt of the delete session response (Delete Session Response), theMME sends TA accept (TA Accept) to the UE. In this TA accept (TAAccept), IP address information, newly assigned to the user, is set andnotified of the UE.

The foregoing description is for the case of using GTPv2 protocolbetween the SGW and the PGW. Similar functions may, however, beimplemented using PMIPv6.

In this case, Proxy Binding Update is used in place of the createsession request (Create Session Request)/delete session request (DeleteSession Request). Also, proxy binding acknowledgement (Proxy BindingAcknowledgement) is used in place of the create session response (CreateSession Response)/delete session response (Delete Session Response).

The sequence for LPGW re-selection is shown in FIG. 11. However, if theabove function is to be implemented, it is necessary for the MME tore-select the PGW at an appropriate timing.

If, when the UE is engaged in packet communication, it is tried tochange the PGW connected to the service network, the information such asthe IP address is changed for the UE's counterpart of communication. Asa result, the packet communication by the UE is disconnected. Thus, inthe sequence operation shown in FIG. 11, it is necessary to re-selectthe PGW when the UE is not engaged in packet communication. That is, PGWre-selection is to be made during the ECM-IDLE time.

FIG. 11 shows the operation when the SGW is changed. However, even incase the SGW is not changed, the basic operation is the same. Themessage sequence, shown in FIG. 11, is explained in terms of messagenames for a case where the communication between the SGW and the PGW isimplemented using GTP protocol. However, similar effects may also beobtained in case the communication between the SGW and the PGW isimplemented using PMIP protocol.

If, in FIG. 11, the MME is substituted by the SGSN, and the eNodeB issubstituted by RNC, the operation is that of PGW re-selection in casethe access network is the UMTS.

In the present exemplary embodiment, as described above, packetcommunication services may be extended by LPGW re-selection as no usertraffic is taken into the EPC. Hence, a mobile communication operator isable to reduce a load of an EPC network apparatus.

Exemplary Embodiment 6

Following describes a sixth exemplary embodiment of the presentinvention will now be described. The configuration of the presentexemplary embodiment is that as shown FIG. 9. The following describesthe operation of the present exemplary embodiment will now be set outwith reference to FIG. 12.

The MME receives a TA update request (TA Update Request) from the UE. Inthe case of the LIPA/SIPTO architecture, a TA update request (TA UpdateRequest) signal is encapsulated in the S1-AP message for communicationfrom the eNodeB to the ME. The eNodeB sends to the MME a notification onthe S1-AP message to the effect that PDN connection may be set based onthe LIPA/SIPTO architecture.

The MME examines whether or not the PGW, the UE in question is connectedto, is appropriate. It is noted that the above mentioned notification onthe S1-AP message that setting of PDN connection by the LIPA/SIPTOarchitecture is possible is by way of illustration only such that it isalso possible for the MME to decide on the necessity for re-selection ofa new PGW based on some other information.

FIG. 12 shows a state in which the UE is connected to PGW (1) (EPSbearer originally established from the UE to the PGW (1)). In case theMME decides that LPGW re-selection is necessary, it sets a cause valuethat urges re-attach (ATTACH) in the TA update request (TA UpdateRequest) and returns a TA update reject (TA Update Reject) to the UE.

The UE is induced by the TA update reject (TA Update Reject) to send theATTACH signal to the MME. This ATTACH signal is also encapsulated in theS1-AP message for transmission. The eNodeB sends to the MME anotification on the S1-AP message to the effect that PDN connection maybe set based on the LIPA/SIPTO architecture.

It is now possible for the MME to newly start up the PGW selectionlogic. As a result, it becomes necessary to re-select LPGW.

FIG. 12 shows an example connection processing to LPGW re-selected. Acreate session request (Create Session Request) from the MME to the SGW(2) and LPGW, a create session response (Create

Session Response) from the LPGW to the SGW (2) and MME, a delete sessionrequest (Delete Session Request) from the MME to the SGW (1), a deletesession response (Delete Session Response) from the SGW (1) to the MMEand a TA update accept from the MME to the UE, are sent.

In the present exemplary embodiment, as described above, packetcommunication services may be extended by LPGW re-selection as no usertraffic is taken into EPC. Hence, a mobile communication operator isable to reduce a load of an EPC network apparatus.

Exemplary Embodiment 7

The following describes a seventh exemplary embodiment of the presentinvention will now be described. The configuration of the presentexemplary embodiment is that as shown FIG. 9. The operation of thepresent exemplary embodiment will now be described with reference toFIG. 13. In the present exemplary embodiment, the regular TA updateprocedure is changed.

The MME receives a TA update request (TA Update Request) from the UE. Itis noted that, in the case of the LIPA/SIPTO architecture, the TA updaterequest (TA Update Request) signal from the eNodeB to the MME isencapsulated in the S1-AP message for transmission.

At this time, a notification is sent on the S1-AP message to the MME tothe effect that PDN connection may be set based on the LIPA/SIPTOarchitecture. It is noted however that the notification sent on theS1-AP message to the effect that PDN connection may be set based on theLIPA/SIPTO architecture is by way of illustration only such that it isalso possible for the MME to decide on the necessity for re-selection ofa new PGW based on some other information.

The TA update accept (TA Update Accept) signal that notifies thecompletion of the TA update procedure from the MME to the UE is added bynew information (PDN in FIG. 13) to urge re-connection of the packetdata network (PDN) which is currently in a connected state. On receiptof the TA update accept (TA Update Accept) signal added by the newinformation (PDN), the UE recognizes the PDN (packet data network) forre-connection, based on the information specified. It is noted that aplurality of PDNs may sometimes be so added. For the PDN in question,the UE starts up the conventional UE requested PDN connection processingor the UE requested PDN connectivity processing to re-connect the packetdata network (PDN).

In this re-connection of the packet data network (PDN), it is possiblefor the MME to newly start up the PGW selection logic, as a result ofwhich it becomes necessary to re-select an optimum PGW.

The operation for the case where the SGW is to be changed has beenexplained with reference to FIG. 13. However, even when the SGW is notchanged, the basic operation remains the same.

In the present exemplary embodiment, as described above, packetcommunication services may be extended by LPGW re-selection as no usertraffic is taken into EPC. Hence, mobile communication operator is ableto reduce a load of an EPC network apparatus.

Exemplary Embodiment 8

The following describes an eighth exemplary embodiment of the presentinvention. The configuration of the present exemplary embodiment is thatas shown FIG. 10. The operation of the present exemplary embodiment willnow be described with reference to FIG. 14.

The SGSN (Serving GPRS Support Node) receives an RA (Routing Area)update request (RA Update Request) from the UE. In the case of theLIPA/SIPTO architecture, the RA update request signal from the NodeB tothe SGSN is encapsulated in a RANUP (Radio Access Network Access Part)message for transmission. The RRC sends to the SGSN a notification onthe RANAP message to the effect that PDN connection may be set based onthe LIPA/SIPTO architecture.

The SGSN examines whether or not the GGSN (Gateway GPRS Support Node),the UE in question is connected to, is appropriate. It is noted that theabove mentioned notification on the RANAP message that PDN connectionsetting by the LIPA/SIPTO architecture is possible is only by way ofillustration. That is, it is also possible for the MME to decide on thenecessity for re-selection of a new PGW based on some other information.

FIG. 14 shows a state in which the UE is connected to GGSN (GTP tunnelconnection is established between UE and GGSN: see ‘GTP Tunnelingoriginally established’ of FIG. 14).

In case the SGSN decides that LGGSN re-selection is necessary, the SGSNsets a reason value (cause value) that urges re-attach (ATTACH) in theRA update request (RA Update Request) to send back an RA update reject(RA Update Reject) signal to the UE.

The UE is caused by the RA update reject (RA Update Reject) signal tosend the ATTACH signal to the SGSN to try to re-attach (ATTACH) to theGPRS network. The SGSN sends an RA update request (RA Update Request) toan HLR (Home Location Register). An insert subscriber data (InsertSubscriber data) is sent from the HLR to the GGSN. The GGSN sends backan insert subscriber data acknowledge (Insert Subscriber data ack)response to the HLR. On receipt of the ack response (ack), the HLR sendsback an RA update response (RA Update Response) to the SGSN. The SGSNsends back an ATTACH accept (ATTACH Accept) to the UE.

The UE then sends a request for activating PDP context (Activate PDPcontext request), requesting PDP (Packet Data Protocol) connection, tothe SGSN.

On receipt of the request for activating PDP context (Activate PDPcontext request), the SGSN decides whether or not the connection toLGGSN is appropriate. When the SGSN decides that the connection to LGGSNis appropriate, the SGSN performs creation of a GTP (GPRS TunnelingProtocol) tunnel to the LGGSN (Create PDP context request). The CreatePDP context request is sent back from the LGGSN to the SGSN, and a PDPcontext activate response (Activate PDP context response) is sent backfrom SGSN to the UE to enable connection between UE and LGGSN.

In the present exemplary embodiment, as described above, packetcommunication services may be extended by LPGW re-selection as no usertraffic is taken into the EPC. Hence, a mobile communication operator isable to reduce a load of a GPRS network apparatus.

The particular exemplary embodiments or examples may be changed oradjusted within the gamut of the entire disclosure of the presentinvention, inclusive of claims, based on the fundamental technicalconcept of the invention. Further, variegated combinations or selectionof elements disclosed herein may be made within the framework of theclaims. That is, the present invention may encompass variousmodifications or corrections that may occur to those skilled in the artin accordance with and within the gamut of the entire disclosure of thepresent invention, inclusive of claim and the technical concept of thepresent invention.

1. A communication method in Selected IP Traffic Offload (SIPTO)architecture, the method comprising: a mobility management entity (MME)sending a first signal for setting re-attachment to a user equipment,when the MME decides that it is necessary to re-select a gatewayapparatus; the user equipment, on receipt of the first signal,transmitting a second signal for re-attachment to the MME; and the MMEreceiving a delete session request from the gateway apparatus andperforming re-selection of a gateway apparatus.
 2. The communicationmethod according to claim 1, wherein the gateway apparatus includes aserving gateway apparatus.
 3. A communication system in Selected IPTraffic Offload (SIPTO) architecture, the system comprising: a mobilitymanagement entity (MME) that sends a first signal for settingre-attachment, when the MME decides that it is necessary to re-select agateway apparatus; a user equipment that, on receipt of the firstsignal, transmits a second signal for re-attachment to the MME; and aplurality of gateway apparatuses, re-allocation thereof controlled bythe MME, the MME receiving a session delete request from the gatewayapparatus and performing re-selection of a gateway apparatus.
 4. Thecommunication system according to claim 3, wherein the gateway apparatusincludes a serving gateway apparatus.
 5. A user equipment in acommunication system by Selected IP Traffic Offload (SIPTO)architecture, wherein the user equipment receives a first signal thatsets re-attachment from a mobility management entity (MME) and transmitsa second signal for re-attachment to the MME, which receives a deletesession response from a gateway apparatus, to cause the MME to performre-selection of a gateway apparatus.